        uint256 userBalance = balanceOf(owner);

        uint256 amountToWithdraw;
        uint256 amountToBurn;

        uint256 currentRate = rate();
        if (staticAmount > 0) {
            amountToBurn = (staticAmount > userBalance) ? userBalance : staticAmount;
            amountToWithdraw = _staticToDynamicAmount(amountToBurn, currentRate);
        } else {
            uint256 dynamicUserBalance = _staticToDynamicAmount(userBalance, currentRate);
            amountToWithdraw = (dynamicAmount > dynamicUserBalance)
                ? dynamicUserBalance
                : dynamicAmount;
            amountToBurn = _dynamicToStaticAmount(amountToWithdraw, currentRate);
        }

        _burn(owner, amountToBurn);
    function _staticToDynamicAmount(uint256 amount, uint256 rate_) internal pure returns (uint256) {
        return amount.rayMul(rate_);
    }
    function _dynamicToStaticAmount(uint256 amount, uint256 rate_) internal pure returns (uint256) {
        return amount.rayDiv(rate_);
    }
